Any long term ROI of above 2.07% will pay PC

Does how you win the money make a difference?

ie if you made £2074 profit on £10,000 over 1000 bets where you had 900 losers and 100 winners, backing mostly at bigger prices.

Compared to making £2074 profit on £10,000 over 1000 bets where you had 400 losers and 600 winners, backing mainly at shorter prices.

Does that make a difference? I worked out that the my commission generated would be much higher in the top example,backing at bigger prices with a much lower SR, to the bottom, backing at short prices with a higher striker rate?

I think you're right. The prices of the winners makes a difference so it can't be pinned down I think

Strike Rate is the key thing i would assume.

Traders are talented position players who look to close out every position without giving value away would be the only people paying it i'd have thought.

Though maybe not under the latest rules.

I can see how you get the 2.07%, you are calculating ROI on net profit divided by wins +losses, but you should be dividing by 2xlosses.
If you are on 60% then the figure on stakes is 2.14%, if on 50% then 2.57% and 40% then 3.23%.
Of course if one is on such a low ROI then one will get bad runs and good runs and at any moment in time the PC is effectively a higher %age except when lifetime winnings are at a high water mark, so one is quite likely to run into PC with a long term ROI of less than this or even negative.
Of course one wont pay the PC except when one's lifetime winnings are over £250k, so the people who will get really hammered are those who used to do well but through increased competition their hit rate has declined significantly.